1. Field of the Invention
The present invention pertains to trailer hitch mechanisms and, more particularly, to an air-operated coupling assembly for releasably attaching a trailer to a truck or to another trailer while preventing relative movement between a drawbar and the coupling.
2. Description of the Related Art
Trailers are attached to heavy-duty trucks and other trailers using a variety of hitch mechanisms. A typical hitch system utilizes a drawbar extending from a trailer having an eye formed thereon that is received over a hook on a hitch. Because fit is not tight, the play between the drawbar and the hitch mechanism allows the drawbar to move rearward and contact the hook when the truck accelerates forward or when the truck stops while moving rearward; and, conversely, the drawbar will move forward and contact the hook when the truck deaccelerates or accelerates rearward.
One method for eliminating the play between the drawbar and the hitch is to push the drawbar into contact with the hitch during operations. FIG. 1 is an exploded view of a known hitch 20 for attachment to a mounting surface 22 on a vehicle (not shown), such as a tractor or trailer. The hitch 20 is fastened to the mounting structure 22 with studs 24 extending from an air chamber 26 and through an adapter bracket 28, then through the mounting structure 22 and into the body 30 of the hitch assembly 20. A thimble 32 is coupled to the air chamber 26 and extends through the adapter bracket 28, the mounting structure 22, and into the hitch body 30.
The hitch 20 includes the aforementioned body 30 having a hook portion 34 extending forward and upward therefrom. A latch 36 is rotatably mounted to the hitch body 30 to move into contact with a top face of the hook 34. A pawl 38 holds the latch 36 in place against the hook portion 34.
A drawbar 40, shown in partial cross section, has an opening or eye 42 formed therein sized and shaped to be slid over the hook portion 34 so that a distal end 44 rests in a space 46 between the hook portion 34 and the hitch body 30.
Referring to the isometric illustration of the hitch 20 in FIG. 2, a shoe 48 is mounted inside the hitch body 30 having a concave face 50 facing towards the hook 34. The shoe 48 is adapted to pivot into contact with the distal end 44 of the drawbar 40 when urged by the thimble 32. The thimble 32 is extended into contact with the shoe 48 by the air chamber 26. Pressurized air acting on a diaphragm in the air chamber forces the thimble 32 to extend away from the air chamber 26 and into engagement with the shoe 48. A spring (not shown) positioned between the shoe 48 and the hitch body 30 urges the shoe away from contact with the drawbar 40 when the air chamber 26 is unpressurized. In other words, the spring pushes the shoe away from the drawbar 40 into contact with the thimble and hence urges the thimble to retract into the unpressurized air chamber 26.
In some applications, the thimble is actuated by an actuator rod 52 (shown in FIG. 1) that is mechanically coupled to the diaphragm in the air chamber 26.
In operation, release of an emergency brake in the tractor causes pressurized air to enter the air chamber 26, thus forcing the actuator rod 52 and the thimble 32 into engagement with the shoe 48. The shoe 48 in turn pivots in the hitch housing 30 into contact with the distal end 44 of the drawbar 40, pushing the drawbar 40 into contact with the hook 34. The pressurized air in the air chamber 26 maintains the shoe 48 in contact with the drawbar 40 to keep the drawbar 40 in constant contact with the hook 34 during operations. This prevents the drawbar 40 from sliding back and forth into contact with the hook portion 34.
In the structure illustrated in FIG. 1, there is a straight linear alignment of the actuator rod 52, thimble 32, and the concave face 50 of the shoe 48. In some installations, there is insufficient room to mount the air chamber 26, and as a result linear alignment of the actuator rod 52 and thimble 32 cannot be obtained. Hence, there is a need for a way to actuate the shoe without having the actuating mechanisms in linear alignment.